The present invention relates to a thermoplastic molding process and apparatus and especially to a thermoplastic process and apparatus using a thermoplastic extrusion die having adjustable gates for varying the thickness of the extruded material, which material is molded as it is passed from the extrusion die.
In the past it has been common to provide a wide variety of molding systems including the molding of a thermoplastic resin or a thermoplastic composite part. In vacuum molding, a slab of heated thermoplastic material is placed on the vacuum mold and a vacuum drawn between the mold and the heated plastic material to draw the plastic material onto the mold. Similarly, a compression molded part feeds a heated slab of thermoplastic material, such as a sheet of material, between two molding forms which compresses the material in the mold.
The present invention is directed towards a molding system for producing a thermoplastic resin of thermoplastic composite parts using either a vacuum or compression mold with parts being fed directly to the molds from an extrusion die while the thermoplastic slab still retains the heat used in heating the resins to a fluid state for forming the sheets of material through the extrusion die.
Prior U.S. Pat. Nos which use thermoforming of material can be seen in the four Winstead patents, Nos. 4,420,300; 4,421,712; 4,413,964; and 3,789,095. The Winstead ""712 and ""300 patents are for an apparatus for continuous thermoforming of sheet material including an extruder along with stretching means and a wheel having a female mold thereon and a plurality of plug-assist means interlinked so as to form an orbiting device having a plug-assist member engaging the sheet material about a substantial arc of wheel surface. The Winstead ""964 patent teaches an apparatus for continuously extruding and forming molded products from a web of thermoplastic material while continuously separating the product from the web, stacking and handling the products, and recycling the web selvage for further extrusion. The apparatus uses multiple mold cavities in a rotating polygon configuration over a peripheral surface of which the biaxially oriented web is continuously positioned by a follower roller interfacing the polygon with a biaxial orientation device. The Winstead U.S. Pat. No. 3,789,095 is an integrated method of continuously extruding low density form thermoplastic material and manufacturing three-dimensional formed articles therefrom.
The Howell U.S. Pat. No. 3,868,209, is a twin sheet thermoformer for fabricating a hollow plastic object from a pair of heat-fusible thermoplastic sheets which are serially moved in a common horizonal plane from a heating station to a mold mechanism at a forming station. The Held, Jr. U.S. Pat. No. 3,695,799, is an apparatus for vacuum forming hollow articles from two sheets of thermoplastic material by passing the sheets of material through a heating zone while in a spaced relationship and between two mold halves. The mold halves are brought together as a vacuum is pulled on each sheet to cause it to conform to the shape of its respective mold so as to mold a hollow article. The Budzynski et al., U.S. Pat. No. 5,551,860, is a blow molding apparatus for making bottles which have rotating molds continuously rotating while aligning one mold at a time with an extrusion die handle for loading the mold. The Hujik U.S. Pat. No. 3,915,608, is an injection molding machine for multi-layered shoe soles which includes a turntable for rotating a plurality of molds through a plurality of work stations for continuously molding shoe soles. The Ludwig U.S. Pat. No. 3,302,243, is another apparatus for injection molding of plastic shoes. The Lameris et al. U.S. Pat. No. 3,224,043, teaches an injection molding machine having at least two molds which can be rotated for alignment with plastic injecting nozzles. The Vismara U.S. Pat. No. 4,698,001, is a machine for manufacturing molded plastic motorcycle helmets and which uses a compression type mold in which a pair of mold halves is shifted between positions. The Krumm U.S. Pat. No. 4,304,622, is an apparatus for producing thick slabs of thermoplastic synthetic resins which includes a pair of extruders, each extruding a half slab strand to a respective roller assembly. The roller assemblies have final rollers which form a consolidation nip between them in which the two half slabs are bonded together.
The present invention is directed towards a continual thermoforming system which is fed slabs of thermoplastic material directly from an extruder forming the slabs of material onto a mold which can be rotated between stations. The thermoplastic material is extruded through an extrusion die which is adjustable for providing deviations from a constant thickness plastic slab to a variable thickness across the surface of the plastic slab. The variable thickness can be adjusted for any particular molding run or can be continuously varied as desired. This allows for continuous molding of thermoplastic material having different thicknesses across the extruded slab and through the molded part to control the interim part thickness of the molded part so that the molded part can have thick or thin spots as desired throughout the molded part.
A thermoplastic molding system includes a thermoplastic extrusion die for the extrusion of a thermoplastic slab. The extrusion die has adjustable die gate members for varying the thickness of the extruded material in different parts of the extruded slab. The thermoplastic extrusion die has a trimmer for cutting the extruded thermoplastic slab from the thermoplastic extrusion die. A plurality of thermoplastic molds, which may be either vacuum or compression molds, are each mounted on a movable platform, such as a rotating platform, for moving one mold at a time into a position to receive a thermoplastic slab being trimmed from the thermoplastic extrusion die. A molded part is formed with a variable thickness from a heated slab of thermoplastic material being fed still heated from the extrusion die. A plurality of molds are mounted to a platform to feed one mold into a loading position for receiving a thermoplastic slab from the extrusion die and a second mold into a release position for removing the formed part from the mold. The platform may be a shuttle or a rotating platform and allows each molded part to be cooled while another molded part is receiving a thermoplastic slab. A thermoplastic molding process is provided having the steps of selecting a thermoplastic extrusion die in accordance with the apparatus adjusting the thermoplastic extrusion die for varying the thickness of the extruded material passing therethrough in different parts of the extruded slab. The thermoplastic material is heated to a fluid state and extruded through the selected thermoplastic die which has been adjusted for varying the thickness of the extruded material in different parts of the extruded slab, trimming the extruded thermoplastic slab having a variable thickness to a predetermined size, and directing each trim slab of heated thermoplastic material onto a thermoforming mold, and molding a predetermined part in the mold so that the molded part is formed with a variable thickness from a slab of material heated during extrusion of the material.